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sw_engine raster: ++ precise alpha multiplying

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previously alpha multiplying operation doesn't have perfect precision,
could loss 1 pixel since it divides 255 values by 256.

This improved operation comply with both precision & performance.
This commit is contained in:
Hermet Park 2021-04-05 17:15:37 +09:00 • committed by Mira Grudzinska
parent 9a1d7ec841
commit 9a40b64261
2 changed files with 11 additions and 7 deletions
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2
src/lib/sw_engine/tvgSwCommon.h
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@ -274,7 +274,7 @@ static inline uint32_t COLOR_INTERPOLATE(uint32_t c1, uint32_t a1, uint32_t c2,
static inline uint8_t ALPHA_MULTIPLY(uint32_t c, uint32_t a) static inline uint8_t ALPHA_MULTIPLY(uint32_t c, uint32_t a)
{ {
return (c * a) >> 8; return ((c * a + 0xff) >> 8);
} }
static inline SwCoord HALF_STROKE(float width) static inline SwCoord HALF_STROKE(float width)

16
src/lib/sw_engine/tvgSwRaster.cpp
View file

@ -851,9 +851,11 @@ bool rasterGradientShape(SwSurface* surface, SwShape* shape, unsigned id)
bool rasterSolidShape(SwSurface* surface, SwShape* shape, uint8_t r, uint8_t g, uint8_t b, uint8_t a) bool rasterSolidShape(SwSurface* surface, SwShape* shape, uint8_t r, uint8_t g, uint8_t b, uint8_t a)
{ {
r = ALPHA_MULTIPLY(r, a); if (a < 255) {
g = ALPHA_MULTIPLY(g, a); r = ALPHA_MULTIPLY(r, a);
b = ALPHA_MULTIPLY(b, a); g = ALPHA_MULTIPLY(g, a);
b = ALPHA_MULTIPLY(b, a);
}
auto color = surface->blender.join(r, g, b, a); auto color = surface->blender.join(r, g, b, a);
auto translucent = _translucent(surface, a); auto translucent = _translucent(surface, a);
@ -872,9 +874,11 @@ bool rasterSolidShape(SwSurface* surface, SwShape* shape, uint8_t r, uint8_t g,
bool rasterStroke(SwSurface* surface, SwShape* shape, uint8_t r, uint8_t g, uint8_t b, uint8_t a) bool rasterStroke(SwSurface* surface, SwShape* shape, uint8_t r, uint8_t g, uint8_t b, uint8_t a)
{ {
r = ALPHA_MULTIPLY(r, a); if (a < 255) {
g = ALPHA_MULTIPLY(g, a); r = ALPHA_MULTIPLY(r, a);
b = ALPHA_MULTIPLY(b, a); g = ALPHA_MULTIPLY(g, a);
b = ALPHA_MULTIPLY(b, a);
}
auto color = surface->blender.join(r, g, b, a); auto color = surface->blender.join(r, g, b, a);
auto translucent = _translucent(surface, a); auto translucent = _translucent(surface, a);